The hypothesis of this proposed research is that the effective release of adsorbed molecules on environmental particles at environmentally relevant surface coverages can be predicted on the basis of quantifiable physicochemical determinants. This hypothesis is based on previous studies from this research group which show that chemical agents formed during combustion and adsorbed on the surfaces of carbonaceous particles can cause adverse biological effects only if released from the surface. Dose at the target site, (e.g., pulmonary epithelium), will be defined by the release of the sorbed molecules that are thermodynamically predisposed to desorption from the surface of the carbonaceous particle. It is proposed that the effective dose can be predicted by the physical and chemical properties of the particle surface, the physical and chemical properties of the molecules, and interaction of the particle-adsorbate complex with alveolar surfactant. The specific aims of the proposed study are to: 1.) Quantify the adsorption of single and dual agents onto carbonaceous particles up to high surface coverages using static methods; 2.) Quantify the physical release of single and dual agents from the surfaces of carbonaceous particles up to high surface coverages into model alveolar surfactant using pseudophase liquid chromatography; 3.) Develop a comprehensive model that will predict the bioavailabilities of biologically active molecules found in carbonaceous particulate matter at environmentally relevant surface coverages.